Head load/unload has been used primarily for removable flexible magnetic disk drives, removable cartridge magnetic disk drives, and portable computer magnetic disk products.
The removable flexible magnetic disk products and removable cartridge magnetic disk products must use head load/unload to remove the head(s) from the disk so that the removable flexible magnetic disk cassette and the removable hard magnetic disk cartridge may be removed from the disk drive. The removable flexible and hard disks are typically low capacity, low performance products, and typically employ a single disk. Thus, the head load/unload requirements are not critical and considerable tolerance is allowed.
Portable computer magnetic disk products are concerned about the potential for "head slap", which may be caused by external shock, e.g., when the computer for housing the disk drive or the disk drive is bumped or dropped. As the result of the external shock, the head slider momentarily lifts from the rest position on the disk and bounces back down on to the surface of the disk. The impact of the head slider on the disk can cause permanent deformation in localized areas of the disk where the slider edge or corner hits the disk, also referred to as "disk dings".
Portable disk drives are normally low capacity, low performance disk drives, having low disk spindle speeds (3600 to 4500 rpm), small disks (2.5" or 1.8" form factors) and a small number of disks (1 to 3). Such portable disk drives are typically designed to allow for low precision and high tolerances.
High end disk drives are having difficulty meeting the conflicting requirements of slider start/stop durability and stiction as fly heights necessarily are reduced to accommodate the need for increased data recording density. Head slider load/unload is one method for relieving these problems. Thus, head load/unload may become widely used in the industry to enable increased recording density with reliable start/stop.
The required high capacities typically require designs to maximize the number of disks in a stack and to reduce the disk spacing as much as possible. Since the heads are positioned between the disks, the head suspensions must be designed to be close to the disk surfaces and thin in vertical dimensions in order to fit between the disks. Thus, head suspension load/unload lift cams for high end disk drives must also be designed to fit between the disks and be close to the surface of the disks. These design requirements, in turn, require high precision and close manufacturing tolerances.
The manufacturing tolerance contributors in the disk to load/unload ramp relative position include ramp base plate to spindle vertical location tolerances, hub to shaft tolerances, and contributors that add to spindle tilt (relative to the base plate).
Variation in the positioning of the load/unload ramps in the vertical direction (the direction of the axis of the stack of disks) also affects the usable amount of recording real estate on the surface of the disks. Specifically, variation in the relative vertical position of the suspension lift location at the ramp varies the horizontal position of the point on the ramp where the slider lifts off the disk. Thus, there is a corresponding variation in the radial position on the disk where the slider lifts off the disk. This variation must be accounted for and results in a radial band on the disk which can be called the load/unload zone. Reducing the variation in the relative vertical positions of the ramp with respect to the disk reduces the variation in the vertical location of the point of the ramp that the suspension contacts and, in turn, reduces the radial width of the load/unload zone on the disk and thus leaves more room for data storage on the disk. This variation must be reduced in order to reduce the size of the landing zone on the disk and thereby increase the size of the recordable recording surface on the disk.
Adjustable load/unload lift cams have been employed for single removable floppy disks or removable hard disk cartridges. An example is illustrated in PCT Published Application WO 96/36045. The vertical adjustment provided is not precise and comprises sliding inclined surfaces. The adjustment is appropriate to the lack of precision required for removable floppy disks or removable hard disk cartridges, and no tool is provided to accomplish a precision adjustment.
What is needed is a means to compensate for the accumulated manufacturing tolerances in positioning of the load/unload lift cam ramps.